This specification generally relates to techniques for generating and recovering watermark images. The watermark images are used to modify unknown source images, e.g., source images that are presented as third-party content in electronic documents.
In a networked environment, such as the Internet or other networks, first-party content providers can provide information for presentation in electronic documents, for example web pages or application interfaces. The documents can include first-party content provided by first-party content providers and third-party content provided by third-party content providers.
Third-party content can be added to an electronic document using various techniques. Some documents include tags that instruct a client computer on which the document is presented to request third-party content items directly from third-party content providers. Other documents include tags that instruct the client computer to call an intermediary service that partners with multiple third-party content providers to return third-party content items selected from one or more of the third-party content providers. In some instances, third-party content items are dynamically selected for presentation in electronic documents, and the particular third-party content items selected for a given serving of a document may differ from third-party content items selected for other servings of the same document.